Role of spherical particles on magnetic field recording in sediments: Experimental and numerical results

We report deposition experiments using spherical glass beads that possess remanent magnetizations stemming from iron impurities. 15g of glass beads with a well-characterized size distribution were loaded in two different sets of tubes with diameters of 2.0 and 3.6cm. Each tube contains identical column heights of de-ionized water, thereby allowing us to assess the effect of sediment concentration on the results (352 versus 90kg/m³[g/l], respectively). The tubes were placed in magnetic fields of variable inclination and intensity in a temperature-controlled environment. The full vector magnetization and sediment accumulation rates were measured upon deposition times ranging from 10min to 10days. Experiments were run in triplicate to evaluate data reproducibility. Together with the lack of magnetic interaction and the absence of clumping, the experiments elucidate an end-member scenario of how sediments acquire remanent magnetizations in the absence of flocculation. Our results show that inclination shallowing, in the range of 7-20° for field inclinations of 30° and 60°, is indeed possible with solely spherical particles. More importantly, we observe a field dependence on the inclination error. Field dependence on the moment acquisition and inclination error both exhibit non-linearity, which may complicate interpretations of relative paleointensity data in paleomagnetic records. A newly developed numerical model, whereby particle collision during settling combined with both rolling and slipping (translation) on the substrate, is consistent with the experimental results.